The present invention relates to a method for estimating a path orientation followed by a movement sensor carrier. It also relates to a corresponding device and computer program.
It applies to the technical field of detecting movements and in particular to the indoor location and following of a moving physical system carrying a movement sensor, for example the location inside a building of a person carrying a device in which such movement sensor is integrated. Among promising technologies, the approach by inertial measurement by means of a movement sensor appears to be the most appropriate for applications to the general public since it is now available with potential users in some cellphones and digital tablets.
The invention therefore applies more particularly to a method for estimating an orientation of a path followed by a carrier of a movement sensor comprising the following steps:                determining an orientation of the movement sensor with respect to the path followed by the carrier,        estimating an orientation of the movement sensor with respect to a fixed reference linked to the terrestrial reference frame by means of measurements supplied by the sensor, and        estimating an orientation of the path followed by the carrier with respect to the fixed reference by means of the determined orientation of the movement sensor with respect to the path and the estimated orientation of the movement sensor with respect to the fixed reference.        
Although open to improvement, all the means necessary for implementing the aforementioned steps, or even the complete following of a path from the determination of its orientation, are well known and technically mastered (measurement of heading, counting of steps, etc.) with the exception of only one: the one making it possible to reliably know the orientation of the movement sensor with respect to the path followed by the physical system being observed, that is to say the carrier of the sensor. This problem of determining the orientation of the movement sensor with respect to the path is difficult to solve, the solutions being rare and unsatisfactory.
Generally, the sensor is then attached to the carrier so that constraining assumptions are made on its relative orientation with respect to the carrier and therefore with respect to the path followed by the carrier. However, this solution is not satisfactory for applications in which the sensor is integrated in a portable device, cellphone or digital tablet, intended to be simply carried without any particular attachment.
For the purpose of being free from these assumptions and constraints, the patent application published under the number US 2012/0072166 A1 discloses a method for estimating at each instant the relative orientation of the sensor with respect to the path. However, this method imposes other no less constraining assumptions. In particular, the method disclosed in this document consists of vertically projecting a reference related to the movement sensor onto the fixed reference related to the terrestrial reference frame. As detailed on pages 2 and 3 of this document, the horizontal angle between this projected reference and the one related to the path is estimated by angular optimization of a horizontal acceleration measured by the sensor.
The assumption imposed by this document is therefore that the horizontal acceleration measured by the movement sensor is maximal in the horizontal direction of the path followed by the physical system being observed. Apart from the fact that this assumption is itself constraining, it makes the taught method not very robust since it is not actually always verified. This is because, in the case of an application of following a person who is moving by walking, though it is true that his feet follow an acceleration generally oriented in the direction of the path, it is not necessarily the same with the other parts of the body of the person being observed. In particular, the general movement of the person, and therefore of a major part of his body, may take place at constant speed, that is to say at zero acceleration, so that the horizontal acceleration measured by the sensor does not reveal the principal movement. Furthermore, with the exception of the feet, the other parts of the body of the person may be affected by parasitic movements not related to the orientation of the path and may give rise to relatively great accelerations: this is for example the case with rocking movements of the arms.
In addition, still in the case of an application of following a person who is moving by walking, the method used in the document US 2012/0072166 A1 does not make it possible to estimate the direction of movement of the person. To do this, other processing operations on the signals measured are used. Finally, another related drawback is the need to record a large number of measurements prior to the computation, a correct estimation of the path followed by the person being obtained only as from around ten steps. This estimation is therefore not carried out in real time.
It may thus be desired to provide a method for estimating a path orientation that at least partly dispenses with the aforementioned problems and constraints.